The present disclosure generally relates to swab-resistant downhole tools and, more particularly, to swab-resistant downhole tools comprising sealing elements at least partially composed of a shape memory polymer.
A variety of downhole tools may be used within a wellbore in connection with producing or reworking a hydrocarbon bearing subterranean formation. The downhole tool may comprise a wellbore zonal isolation device capable of fluidly sealing two sections of the wellbore from one another and maintaining differential pressure (i.e., to isolate one pressure zone from another). The wellbore zonal isolation device may be used in direct contact with the formation face of the wellbore, with casing string, with a screen or wire mesh, and the like.
Typically, the wellbore zonal isolation device will be introduced and/or withdrawn from the well on a tool string (i.e., a mechanical connection to the surface), such as a tubular string or wireline during certain procedures involved in completion and/or workover operations. The tool string is then introduced into the wellbore concentrically through another tubular conduit, which may be the wellbore itself, casing, or a larger inner diameter production or work string. In other examples, the wellbore zonal isolation device may be pumped into the well, such as by using hydraulic forces to propel the device in or out of the wellbore.
The wellbore zonal isolation device may comprise a body and a sealing element disposed thereon which is traditionally manipulated by hydraulic, mechanical, or electric means to cause the sealing element to expand outwardly into a sealing engagement along the inner diameter of the second or outer conduit, such as the inner smooth wall of casing or the formation face of the wellbore. In such “set” position, the sealing element of the downhole tool will prevent transmission of fluids there across to isolate one portion of the wellbore from another portion.
It may be desirable to run the downhole tool into and out of the well as quickly as possible, in order to reduce the time of a trip into and/or out of the hole and to thereby reduce labor and other operational costs. In many cases, a trip into or out of the wellbore is extended to avoid “swabbing” of the sealing element onto the inner diameter of the outer conduit, casing, or formation face. It is believed that when fluid within the wellbore flows over the sealing element during movement of the tool string, a higher velocity fluid on the outside of the sealing element. This causes a pressure drop that urges the sealing element outward to form a temporary seal with the face of the outer conduit. When so sealed, the tool string, when moved, swabs or carries fluid with it and can cause the wellbore zonal isolation device to prematurely activate or damage or destroy the sealing element. This, in turn, requires a substantial reduction in the rate of movement of the tool string through the wellbore, as much lower run-in speeds must be used in order to avoid swabbing any parts of the wellbore zonal isolation device.